Where a cylindrical member rotates within a complementary cylindrical bore, the useful life of the parts can be extended by providing a hardened wear ring between the parts. For example, machines used to cut hard surfaces such as concrete and asphalt have a rotatable cutting wheel with a plurality of cutting tools mounted on the wheel which are moved against a hard surface to advance the cut. Each of the cutting tools has a cylindrical shank which is rotatably mounted in a complementary cylindrical aperture in a tool holder. As disclosed in my co-pending application, Ser. No. 09/121,726 filed Jul. 24, 1998, now U.S. Pat. No. 6,164,728 the useful life of a tool and the tool holder can be extended by providing a tungsten carbide tubular wear ring at the forward end of the aperture in the tool holder.
It is customary to use a braze to retain parts, such as a tungsten carbide tubular wear ring fitted in a countersink at the end of a cylindrical aperture. The brazing process consists of providing a plurality of rings of braze material which are fitted between the inner surface of the countersink and the outer surface of tubular sleeve. The rings of braze material prevent the hardened ring from becoming seated within the countersink until the braze material is heated and melts, after which the ring can be urged into the countersink until it has become seated. After the parts cool, a substantial portion of the braze material should remain between the inner surface of the countersink and the outer surface of the wear ring to retain the parts in the assembled relationship.
I have found, however, that when the braze material melts and a tungsten carbide wear ring is urged into a countersink as described above, most of the liquefied braze material flows into the cylindrical bore leaving an insufficient amount of braze material to retain the parts in the assembled relationship. When a tungsten carbide insert is brazed into a countersink around the bore in a tool holder, as described above, it has been found that the braze will fail when the tool is subjected to the forces required to cut hard material such as concrete or asphalt. An improved method is therefore needed for brazing a tungsten carbide tubular part in nested relationship with a countersink in a metal part.
Briefly, the present invention is embodied in a method of assembling a tungsten carbide tubular part in coaxial relationship with the bore of another part where the end of the tubular part nests into the second part.
In accordance with the present invention, to braze a tungsten carbide tubular part into a countersink in a metal body having a coaxial bore therein, a plurality of rings of braze material are needed. The rings of brazing material have an inner diameter at least equal to the inner diameter of the tungsten carbide tubular part and an outer diameter which is less than the inner diameter of the countersink. The parts are arranged in coaxial relationship with the rings of braze material and a viscous flux positioned between the complementarily shaped surfaces of the parts to be bonded together.
In a first embodiment of the invention a compressible tubular sleeve (such as a split ring) made of a soft material having an outer diameter which is a little larger than the inner diameter of the cylindrical bore in the metal body is press fitted into the bore of the metal body. The rings of braze material are fitted over the compressible sleeve, then the tungsten carbide wear ring is fitted around the compressible sleeve and against the rings of braze material. The flux is applied to facilitate the brazing process. The assembled parts are thereafter heated, preferably by induction using a channel type coil, causing the braze material to melt. After the braze material has melted the tubular part is urged into nested relationship in the metal body. The parts are orientated so that gravity will urge the parts together and the braze material is retained between the parts by the tubular sleeve of soft metal between the tungsten carbide tubular part and the metal body.
As the braze material melts, the parts are vibrated at about 2500 cycles per minute to agitate the braze material so that heat is evenly distributed throughout and to properly seat the tungsten carbide wear ring with respect to the countersink in the metal body.
The vibration of the parts continues until the parts exit the channel coil, which is typically about six feet long. The parts are allowed to cool until the braze material hardens, after which all the parts will be bonded together. Thereafter, the soft metal of the tubular sleeve can be removed in a machining process. Following the removal of the tubular sleeve, the metal body and the tungsten carbide tubular part will be retained together by the braze remaining between them.
In a second embodiment of the invention, a solid tapered plug made of soft metal is inserted into the bore of the metal body and the bore of the tubular member. The taper of the outer wall of the plug is very gradual and the maximum outer diameter thereof is less than that of the inner diameter of the bore of the tubular member such that when it is inserted into the bore of the metal body it will bind against the inner wall of the bore at the base of the countersink. As with the first embodiment, the parts are heated until the braze material melts and then are vibrated until the assembly exits the channel coils. The parts are then allowed to cool until the braze material hardens, after which the metal plug can be machined out.